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Data Communication & networking

This blog is for undergraduate/graduate students who require some basic information about their subjects or any other topic related to data communication.

Sunday, 27 March 2011

Channel allocation techniques

Channel Allocation Techniques:

Static Channel Allocation (Synchronous):

With static Channel Allocation, a specific capacity is dedicated to a connection;

this is the same approach used in circuit switching, frequency-division multiplexing (FDM), and synchronous time-division multiplexing (TDM). Such techniques are generally not optimal in LANs and MANS because the needs of the stations

are unpredictable.

If any connection is not transferring information, then the channel is wasted which is allocated to particular connection. Therefore it is better for bulky and heavy data.

Dynamic Channel Allocation (Asynchronous):

In dynamic channel allocation, capacity is given whenever there is any need.

It is divided into 3 groups,

a)ROUND ROBIN:

With round robin each turn is given the opportunity to transmit. During that opportunity the station may decline to transmit or may transmit subject to a specific upper bound.

When many stations have data to transmit, round robin technique can be efficient. If only a few stations have data to transmit, then, there is a considerable overhead in passing the turn from station to station, because most of the stations can’t transmit but simply pass their turns.

b) RESERVATION:

It is used for stream traffic, in reservation techniques time on the medium is divided into slots, much as with TDM. Reservation can be made in centralized or distributed fashion.

c) CONTENTION:

It is used for bursty traffic, with contention, no control is exercised to determine whose turn it is, all stations contend for time in a way that can be.